More questions than answers

SPACE CENTER, Houston -- One week after the space shuttle Columbia broke apart as it streaked over Texas just minutes from home, NASA still has more questions than answers.

Searchers have recovered remains of all seven astronauts and more than 12,000 shards of metal, wires and debris that rained down across two states. But the findings so far have yielded few clues.

The most significant discovery has been a 2-foot section of shuttle wing, including the carbon-covered leading edge designed to protect Columbia's insulating tiles as the spacecraft heats to 3,000 degrees re-entering the atmosphere.

If that section came from the troubled left wing, where temperatures surged in the shuttle's final moments and sensors failed in rapid sequence, it could provide hard evidence of what went wrong.

Investigators hadn't yet determined which wing the fragment belonged to, but should know "in relatively short order," NASA Administrator Sean O'Keefe said Saturday after a memorial service at Louisiana's Barksdale Air Force Base, where pieces of the shuttle are being stored.

And in a development late Saturday, NASA officials confirmed that Defense Department radar shows an object or material coming off the shuttle Columbia as it orbited Earth about one day after its Jan. 16 launch.

This kind of signal could represent a meteorite impact, but NASA spokesman Kyle Herring, in Houston, emphasized that its true significance is not yet known. "The Department of Defense has provided the report to NASA, and we're assessing it."

Investigators are looking closely at the shuttle's inflight schedule, he said, in order to determine whether the debris might have come from something benign, such as a routine dump of waste water or other supplies. They are also looking at data from instruments aboard the shuttle that might have registered a sudden vibration or other change in inflight conditions that could have resulted from an impact.

NASA and defense officials have long been concerned about the hazards of space junk. The U.S. Space Command tracks some 9,000 pieces of manmade debris from defunct spacecraft and the like. When encountered at orbital velocities typically around 17,500 mph, a tiny paint chip can leave a gouge.

A report earlier had warned of possible serious damage from a meteroid impact on the leading edge of a shuttle wing, and such an impact was already on the investigators' list of potential causes of the accident.

In the shuttle's final eight minutes the morning of Feb. 1, temperatures surged in the left landing gear compartment, and the brake lines began overheating one by one. Sensors began showing overheating across other areas of the left wing and adjoining fuselage. Then Mission Control lost all contact and Columbia broke apart.

Investigators are considering every possible scenario, from the impact of a large chunk of hard insulating foam that hit the shuttle seconds after liftoff Jan. 16, to a deadly bull-eye's strike by a piece of space junk, to a lightning-like electrical phenomenon in the upper atmosphere.

The seemingly innocuous piece of foam -- once NASA's focus, then all but discarded -- is back at the heart of the mystery.

The 21/2-pound chunk of insulation, measuring 20 inches by 16 inches by 6 inches, broke off Columbia's external fuel tank 81 seconds after liftoff and smacked into the left wing, where the sensors later failed during the shuttle's return.

Engineers studied the impact while Columbia was in orbit and concluded it posed no safety threat. Now they're redoing their analyses, in excruciating detail, to see if they might have missed anything.

It's also possible that something more than the foam chunk -- such as ice or maybe hardware -- came off the fuel tank or booster rockets and ricocheted into Columbia.

Imagery experts are poring over a high-resolution photo taken by an Air Force telescope a minute or two before Columbia broke apart; some have suggested the leading edge of the left wing looks as if it could be damaged, and the photo shows a streak that could be a fiery plume trailing the wing.

Shuttle program manager Ron Dittemore acknowledges confusion, misinformation and "even some second-guessing on all of our parts" in the past week.